m3core/src/time/Common/Time.i3

 Copyright (C) 1989, Digital Equipment Corporation 
 All rights reserved. 
 See the file COPYRIGHT for a full description. 
 Last modified on Thu Dec  9 09:55:13 PST 1993 by mcjones 
      Modified on Thu Oct 11 22:04:09 1990 by muller 
 Based on the Modula-2+ Time.def, designed by Roy Levin. 


 A Time.T represents a moment in time, reckoned as a number of
   seconds since some epoch or starting point.
   \index{time!of day}
   \index{time!Time interface@{\tt Time} interface}



INTERFACE Time;

TYPE T = LONGREAL;

PROCEDURE Now(): T;

 Return the current moment in time. 

VAR (*CONST*) Grain: LONGREAL;

 If a thread performs t0 := Time.Now(); t1 := Time.Now(), then
   either t1 = t0 or t1 >= t0 + Time.Grain.  Grain always lies
   in the half-open interval (0..1] and is usually no larger than
   one sixtieth of a second.  

END Time.

 There are a variety of timekeeping needs, and Time.Now may not
   satisfy all of them.  It is intended to be useful for recording times
   and measuring intervals arising during the execution of computer
   programs with a resolution comparable to human reaction times.


   The epoch for a Time.T varies from one operating system to
   another.  To determine the epoch, call Date.FromTime(0.0D0,
   Date.UTC).  Note that communicating a Time.T between systems,
   say via remote procedure call or pickles, is likely to be a bad
   idea.
   \index{epoch}


   In many computers, Time.Now is implemented with the technology 
   of an inexpensive wristwatch, and is therefore likely to suffer 
   from similar errors: the rate may vary, and the value may be changed 
   by a human operator. 


   The Thread interface contains procedures that delay the execution
   of the calling thread for a specified duration.  The Tick
   interface provides access to a clock with subsecond resolution.